Various desirable properties have been required for adhesives. Recently, with the increase of the kind of objects to be adhered and the availability of high-speed adhering machines, adhesives which are suitable for the joining of a wide range of materials, quickly showing adhesion power after adhesion, and which are excellent in the so-called initial adhesion properties have been desired.
As an adhesive meeting such requirements, a vinyl acetate-ethylene copolymer emulsion having a high solids content is known.
For example, a vinyl acetate-ethylene copolymer emulsion having a solids content of from 45 to 60% by weight is described in JP-B-52-34650 (the term "JP-B" as used herein means an "examined Japanese patent publication"). Also, JP-B-42-22692 describes a process of producing a vinyl acetate-ethylene copolymer emulsion having a solids content of up to 70% by weight by using a polyoxyethylene-polyoxypropylene block copolymer as a surface active agent. Furthermore, JP-B-43-17538 describes a process of obtaining a vinyl acetate-ethylene copolymer emulsion having a solids content of from 60 to 70% by weight by using a surface active agent having an HLB (hydrophilic-lipophilic balance) of from 3 to 8 as an emulsifying dispersant before the polymerization reaction and adding a surface active agent having an HLB of at least 8 during the polymerization.
Furthermore, JP-A-60-1272 describes polyvinyl acetate or vinyl acetate-ethylene copolymer emulsion having a solids content of from 55 to 70% by weight using specific polyvinyl alcohol of a low polymerization degree having an average polymerization degree of from 20 to 300 and having modified polymer terminals as an emulsifying dispersant. (The term "JP-A" as used herein means an "unexamined published Japanese patent application"). Moreover, JP-A-63-223053 describes a vinyl acetate-ethylene copolymer emulsion having a solids content of from 65 to 70% by weight and a viscosity of not higher than 3,500 cps at a solids content of 65% by weight by using polyvinyl alcohol and a surface active agent in amounts of from 2 to 4% by weight and from 1 to 4% by weight, respectively to a vinyl acetate monomer as emulsifying dispersants.
On the other hand, with the increase of the wide use of hydrophobic materials such as plastics, water-repellent papers, resin-coated papers, etc., as materials to be adhered using adhesives; and, with the development of increased high-speed adhering machines, the need for increasing the speed at which adhesives show adhesion power of, that is, the requirement for the initial adhesion properties of adhesives, has been further enhanced. Furthermore, adhesives have recently been required for adhering various kinds of materials, including the aforementioned hydrophobic materials, and to give a high adhesion strength under various conditions. Also, it is, as a matter of course, necessary that such adhesives can be produced in an industrial production step without being accompanied by any inconvenience.
Adhesives meeting the aforesaid requirements have not yet been developed, including the aforesaid conventional techniques.